> Considering that there are over 300 million, yes million, people in China who do not speak Mandarin

I don't think your numbers are right. Tibet has 4 million population. Xinjiang has 20 million, among which 50% are Han. Those are only 2 provinces where I can think of that doesn't require Mandarin to get by in certain area.

The rest of China, at least, could understand Mandarin without problems.

You're just going by intuition, which can be misleading.

Guangdong province alone is 100 million people. Some of whom are Mandarin speakers (1st or 2nd or 2nd+ language). But many are not, not even as 2nd or 2nd+ language speakers. And their predominant language is Cantonese. Many people grew up before mandatory Mandarin education was instituted. There's a similar situation in other huge provinces all around China, especially southern China.

I would say assuming people from Guangdong province, and majority of them don't speak Mandarin is an exaggeration to great extent. Of course they do, it is imperfect with heavy accent. But I won't go that far claiming they don't speak Mandarin, as if saying all English speakers in India don't count, that is just hilarious.

I never made any such claims. This kind of poor quality conversation is not worth engaging in.

It is definitely your claim about the 300 million Chinese that they don't speak Mandarin, that is why the whole conversation happens. Otherwise, it won't add up, even assume majority of Guangdong province don't speak Mandarin at all.

Tibetan parts of Sichuan have many non-mandarin speakers, though these are technically a part of greater Tibet anyways.

If you mean that these 300 million do not have Chinese as the first language https://en.wikipedia.org/wiki/Languages_of_China then it would be correct. But every kid growing up in China has to learn Chinese in school (plus TV etc).

Wrong. A lot of people grew up before this started. And no, I removed the Mandarin-as-an-additional-language people from the number already. (Mandarin 1st + Mandarin as a 2nd or 3rd languages speakers) = 1.1 billion. Population of China, 1.4 billion. 1.4 billion minus 1.1 billion is 300 million.

I’ve run into old people in China who don’t speak a word of mandarin, especially in Tibetan areas. They get the kids to translate for them.